The following background description constitutes a description of the background to the present invention, and thus need not necessarily constitute prior art.
Engines, such as for example engines comprised in vehicles or ships, are usually equipped with an exhaust treatment system for purification of exhausts created during combustion in the engine. In connection with increased government interests concerning pollution and air quality, primarily in urban areas, emission standards and regulations regarding emissions from combustion engines have been drafted in many jurisdictions.
Such emission standards often consist of requirements defining acceptable limits of exhaust emissions from combustion engines in, for example, vehicles. For example, emission levels of nitrogen oxides NO, hydrocarbons CxHy, carbon monoxide CO and particles PM are often regulated by such standards for most types of vehicles. Vehicles equipped with combustion engines typically give rise to such emissions in varying degrees. In this document, the invention will be described mainly for its application in vehicles. However, the invention may be used in substantially all applications where combustion engines are used, for example in vessels such as ships or aeroplanes/helicopters, wherein regulations and standards for such applications limit emissions from the combustion engines.
In an effort to comply with these emission standards, the exhausts caused by the combustion of the combustion engine are treated (purified) in an exhaust treatment system. Such exhaust treatment systems often comprise at least one particulate filter, which is arranged to catch particles, such as for example soot particles, in the exhaust stream.
With a well-functioning particulate filter, a sufficiently large portion of the particles in the exhaust stream are caught up in the particulate filter, so that the requirements in the emission standards may be fulfilled. However, the caught up particles are stored in the particulate filter, impacting its filtering function, and accordingly its ability to catch particles. At a certain storage level for the particulate filter, the filter needs to be purified, which may be achieved with a regeneration of the filter. In order to find out when the regeneration should be carried out, according to prior art a pressure difference over the particulate filter was measured. Based on this measurement, a regeneration of the particulate filter was activated where needed. It is, for example, possible to use models for soot build-up, soot oxidation and ash intercalation in the particulate filter, in order to determine when a regeneration should be activated. In prior art, a soot sensor in the exhaust pipe has also been used for vehicles in some markets, in order to measure the particulate mass in the exhaust pipe.
There is also a risk that the particulate filter may be damaged, worn and/or otherwise break, whereby its ability to catch particles may also deteriorate. According to prior art technology, measurements of the pressure difference over the particulate filter, in order to determine whether the particulate filter is intact or whether it is damaged/broken, have been used for on board diagnostic (OBD; On Board Diagnostic). According to the regulatory framework for vehicles meeting the Euro VI requirements for heavy goods vehicles, there is a requirement that an error code must be generated in case of a 40% reduction of the pressure difference in relation to a reference filter, and over a given measuring cycle. Thus, an OBD code indicates whether the particulate filter is damaged/broken. For vehicles equipped with a soot sensor in the exhaust pipe, the soot sensor may be used also at the determination of whether the particulate filter is damaged, worn or otherwise broken by way of measuring the particulate mass in the exhaust pipe with the soot sensor.